#include <fstream>
#include <vector>
#include <stack>
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
const int NMAX = 100004;
vector <pair<int, int> > v[NMAX];
vector<int> solutie;
stack<int> stiva;
int viz[5*NMAX], n, m;
int main()
{
    f>>n>>m;
    for (int i=1;i<=m;i++)
    {
        int x,y;
        f>>x>>y;
        v[x].push_back(make_pair(y,i));
        v[y].push_back(make_pair(x,i));
    }
    for (int i=1;i<=n;i++)
    {
        if (v[i].size()%2==1)
        {
            g<<"-1";
            return 0;
        }
    }
    stiva.push(1);
    while (!stiva.empty())
    {
        int nod=stiva.top();
        if (v[nod].size()==0)
        {
            solutie.push_back(nod);
            stiva.pop();
        }
        else
        {
            int edge=v[nod].back().second;
            int y=v[nod].back().first;
            v[nod].pop_back();
            if (!viz[edge])
            {
                viz[edge]=1;
                stiva.push(y);
            }
        }
    }
    for (int i=0;i<solutie.size()-1;i++)
        g<<solutie[i]<<" ";
}